MySQL-关于联接的特定列? [英] MySQL - specific columns on join?
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问题描述
进行联接时(内部,左外部,右外部或其他),如何指定表中的哪些列联接到原始表中?
When making a join (inner, left outer, right outer or whatever), how can I specify which columns on the table to join into the original table?
请考虑以下示例:
SELECT FirstName FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
这将从用户中选择名字,但从提供者中选择所有内容.如何指定结果集中应包含提供者的哪些部分?
This would select FirstName from user, but select everything from Provider. How can I specify which parts of Provider should be included in the resultset?
推荐答案
这将在最终结果集中仅包括User.FirstName
和Provider.ProviderID
:
This will only include User.FirstName
and Provider.ProviderID
in the final resultset:
SELECT User.FirstName, Provider.ProviderID FROM User LEFT OUTER JOIN Provider ON User.ProviderID = Provider.ID
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